Writing an arbitrary non-periodic pattern using interference lithography

Abstract

We propose a technique to write non-periodic patterns using interference lithography. Arbitrary patterns in one and two dimension are constructed by continuous scanning of multiple coherent sources at various incident angles and intensities.     

Retrieving two-dimensional information of the subwavelength variation from far-field irradiance

An eigenvalue-problem approach of blind deconvolution is developed to retrieve the information of two-dimensional subwavelength variation from far-field irradiance with an embedded-aperture configuration with three detectors. A reference signal has been implemented to determine the scaling issue, and hence it allows the exact order of magnitude of the retrieved signals to be estimated correctly. It is shown that the subwavelength variations of a two-dimensional aperture can be identified with a precision of better than a 1% error ratio.     

Nonlinearities of an aperture-limited in-line far-field hologram

In several papers, effects of film nonlinearity have been studied considering the off-axis holography. In this analysis, the case of the in-line far-field holography is considered. It is shown that the finite aperture effects influence both the number of extrema in the intensity distribution of an image and the edge smear of this image, while the nonlinearity produces a decrease of the contrast.     

Modeling of two-dimensional random fields

This paper presents a method of conditional stochastic modeling of two-dimensional fields which can be used to predict values at certain field points at a given time, based on field values at other locations at the same time and on data about second order field moments at given points. For computer simulations, the Gaussian truncated distributions are used. The aim of this work is also to present a derivation of a formula for the probability density of an n-dimensional random variable with the Gaussian conditional truncated distribution. As a numerical example, a soil contamination field described by correlation functions corresponding to the white noise field, the Shinozuka field and the Markov field is analyzed. The acceptance-rejection method is applied to generate covariance matrices and vectors of field values. Then, conditional expected field values for adequate correlation functions are calculated.     

Omnidirectional ADE antenna with a GO-shaped main reflector for an arbitrary far-field pattern in the elevation plane

This work presents a formulation for shaping the main reflector of a dual-reflector antenna designed to offer an omnidirectional coverage with an arbitrary radiation pattern in the vertical plane. The subreflector is generated by an axis-displaced ellipse and the main reflector is shaped to achieve a prescribed far-field radiation pattern. The shaping procedure is based on geometrical optics (GO) principles. Two distinct far-field ray structures are investigated. The GO-shaping results are validated by an analysis using the accurate method of moments technique.     

Fabrication of two-dimensional superposed microstructure by interference lithography

In this paper, we report the basic theory and method of single exposure interference lithography (IL) to fabricate two-dimensional (2D) superposed microstructures. Distribution of six-beam interference intensities with different azimuth angle is discussed, and 2D superposed microstructures with different periodic constants are obtained by computer simulations. The experiment results using CHP-C positive photoresist show a 2D superposed photonic crystal composed of a periodically repeated hexagonal pattern of hexagonal lattice cells, which is in close agreement with the computer simulation. Fabrication of a superposed structure by single exposure IL paves the way for studying 2D photonic crystal fabrication, surface lasing, optical waveguides, and so on.     

Growth of cracks under far-field cyclic compressive loads: Numerical and experimental results

Crack growth from a notch tip, under the influence of fully compressive far-field cyclic loads, is investigated both numerically and experimentally in notched specimens of a lower strength steel and an aluminum alloy. Such cracks, emanating from the root of the notch, progressively decelerate until complete crack arrest occurs. Analyses of the stress state along the crack plane indicate that while the extent of the residual tensile stress field diminishes with an increase in crack length, there is a progressive increase in crack closure during crack advance. Approximate numerical calculations of the crack closure loads are in reasonable agreement with experimental results.     

Phase retrieval from experimental far-field intensities by use of a Gaussian beam

The noniterative phase-retrieval method by use of Gaussian filtering is applied to the reconstruction of phase objects from experimental far-field intensities. In this method, the complex amplitude of transmitted light through an object is reconstructed from three far-field intensities, which are measured with the modulation of the object by laterally shifted and unshifted Gaussian filters. In the experiment, the amplitude of a Gaussian beam illuminating objects is utilized as a Gaussian filter, and, as the phase objects, a converging lens with a small exit pupil and a plastic fiber immersed in optical adhesive are used. The experimental results show that the Gaussian beam of a laser is capable of retrieving the phases of those objects with the accuracy of the range from approximately 1/10 to 1/4 of the laser's wavelength.     

Controlled two-dimensional pattern of spontaneously aligned carbon nanotubes

We report a simple solution process to form controlled patterns of aligned single-walled carbon nanotubes on solid substrates. The essential step of the process is to deposit a dilute solution of DNA-wrapped carbon nanotubes (DNA-CNTs) on a SiO(2) surface covered with a thin hydrophobic layer. This leads to deposition of fully aligned CNTs. The alignment pattern can be controlled by metal electrodes in the deposition region and can be quantitatively modeled by the behavior of a quasi-two-dimensional DNA-CNT nematic phase near the solution/SiO(2) interface. These results point to the possibility of rational design and economical fabrication of CNT alignment patterns on solid substrates.     

Bifurcation of crack pattern in arrays of two-dimensional cracks

Theoretical calculations based on simple arrays of two-dimensional cracks demonstrate that bifurcation of crack growth patterns may exist. The approximation used involves the dipole asymptotic or pseudo-traction method to estimate the local stress intensity factor. This leads to a crack interaction parametrized by the crack length/spacing ratio =a/h. For parallel and edge crack arrays under far field tension, uniform crack growth patterns (all cracks having same size) yield to nonuniform crack growth patterns (bifurcation) if is larger than a critical value _cr. However, no such bifurcation is found for a collinear crack array under tension. For parallel and edge crack arrays, respectively, the value of _cr decreases monotonically from (2/9)^1/2 and (2/15.096)^1/2 for arrays of 2 cracks, to (2/3)^1/2/ and (2/5.032)^1/2/ for infinite arrays of cracks. The critical parameter _cr is calculated numerically for arrays of up to 100 cracks, whilst discrete Fourier transform is used to obtain _cr for infinite crack arrays. For infinite parallel crack arrays under uniaxial compression, a simple shear-induced tensile crack model is formulated and compared to the modified Griffith theory. Based upon the model, _cr can be evaluated numerically depending on (the frictional coefficient) and c ₀/a (c ₀ and a are the sizes of the shear crack and tensile crack, respectively). As an iterative method is used, no closed form solution is presented. However, the numerical calculations do indicate that _cr decreases with the increase of both and c ₀/a.     

Modeling of a ferromagnetic two-dimensional electron gas device

We present a realistic modeling of ballistic electron transport in a hybrid ferromagnetic (FM) two-dimensional electron gas (2DEG) device, consisting of an FM gate on an AlGaAs-GaAs or AlSb-InAs high electron mobility transistor (HEMT) heterostructure. The carriers within the 2DEG are spin-polarized by a combination of magnetic and electrostatic barriers. The magnetic barriers are supplied by a composite FM gate, consisting of two domains made of magnetically hard and soft materials. This gate arrangement breaks the antisymmetry of the fringe B field, and results in a finite spin polarization of the 2DEG current. The B field strength is calculated by considering the pole strength at the gate surfaces and domain boundary, and is significantly weaker than normally assumed. We obtain parameters such as the electrostatic barrier height, Fermi level, and carrier concentration within the 2DEG by a finite-element Poisson calculation, which is self-consistent with the Fermi-Dirac distribution. We calculate the transmission probability and conductance through the 2DEG from these parameter values, assuming a single particle effective mass Hamiltonian and purely ballistic transport. We show that the spin polarization ratio P/sub G/ is extremely sensitive to the gate bias and HEMT doping concentration. However, the maximum P/sub G/ is extremely low for AlGaAs-GaAs (0.003%) and even for AlSb-InAs (0.12%) devices, despite a large Lande g factor. These values are many orders of magnitude smaller than previous predictions of close to 100% polarization, obtained by using simpler models.     

Modeling and simulation of two-dimensional consolidation for thermoset matrix composites

A finite element method is developed to solve two-dimensional consolidation problems for composites manufacturing. The consolidation governing equations, one for solid stress and one for fluid pressure, are derived using a local volume averaging approach, and the two equations are strongly coupled. A special anisotropic, hyperelastic constitutive equation is developed for the solid stress. This equation matches Gutowski's model for consolidation transverse to the fibers, and has a high stiffness parallel to the fibers. An updated Lagrangian method is used to solve the equations, using implicit time integration and a successive substitution method. The code is applied to several case studies to explore two-dimensional consolidation effects. A free edge affects the thickness profile during consolidation, but the final thickness can still be uniform. This effect is substantial in the region close to the edge, and it propagates progressively from the edge toward the center. Simulations were also performed for laminates that bend to form a corner. The corner is thicker than the flat region after consolidation. Wiggles, similar to fiber buckling, arise at low values of shear modulus when using a male mold. Large values of the solid shear modulus cause the corner effect to extend far into the adjacent flat region. The length of the flat region also affects the consolidation of the corner.     

Properties of far-field fluorescence from an ensemble of interacting Sr atoms

We systematically investigate the far-zone fluorescence from a number of laser-driven two-level atoms with the cooperative effects stemming from the virtual exchange of photons between identical atoms. Due to the large interaction-induced energy level shifts, i.e. the collective Lamb shifts, both atomic excitation and photon emission do not maximize at the resonant light-atom coupling. In addition, the long-range dissipative interactions among atoms lead to the disproportion between the atomic excitation and the photon emission. Moreover, we discuss the temporal properties of the far-field fluorescence light from the atomic ensemble. The first-order correlation function indicates a damped light-atom dynamics combined with a strong background of the elastic photon scattering. The second-order correlation function illustrates that in the weak-excitation limit the scattered light exhibits the nonclassical photon antibunching behavior, while the bunched photons arrive at the photodetector in the saturated-excitation limit.     

Theoretical and experimental evaluation of a two-dimensional composite matrix array

A theoretical and experimental performance appraisal of a two-dimensional, ceramic-epoxy composite matrix array employing 1-3 connectivity is presented. The linear systems approach is used for temporal and spatial simulation of array performance, with specific regard to three-dimensional synthetic aperture imaging in a fluid load medium. Manufacture and experimental evaluation of a prototype array structure, operating at 1.2 MHz and comprising 100 elements arranged as a 10 by 10 matrix, is described. Close agreement between theory and experiment is obtained, providing a clear indication that the low crosstalk, uniformity, and wideband characteristics of composite array elements offer excellent prospects for such imaging applications.     

Modeling and experimental evaluation of an automotive air conditioning system with a variable capacity compressor

A steady state computer simulation model has been developed for refrigeration circuits of automobile air conditioning systems. The simulation model includes a variable capacity compressor and a thermostatic expansion valve in addition to the evaporator and micro channel parallel flow condenser. An experimental bench made up of original components from the air conditioning system of a compact passenger vehicle has been developed in order to check results from the model. The refrigeration circuit was equipped with a variable capacity compressor run by an electric motor controlled by a frequency converter. Effects on system performance of such operational parameters as compressor speed, return air in the evaporator and condensing air temperatures have been experimentally evaluated and simulated by means of developed model. Model results deviate from the experimentally obtained within a 20% range though most of them are within a 10% range. Effects of the refrigerant inventory have also been experimentally evaluated with results showing no effects on system performance over a wide range of refrigerant charges.     

干扰存在时被动声呐工作背景建模与分析

在实际应用中,声呐的工作背景除了各向同性背景噪声外,通常还会存在干扰。干扰存在时经典的被动声呐方程存在一定的局限性。在经典被动声呐方程的基础上,讨论了干扰对被动声呐工作背景的影响。提出了一种更加实用的工作背景模型,并详细分析了波束域的工作背景模型,应用此背景模型对经典被动声呐方程进行了修正,修正后的方程可用于干扰存在时被动声呐的性能预报。最后通过不同干噪比条件下的仿真验证了波束域工作背景模型的正确性。提出的工作背景模型可为被动声呐设备在干扰存在条件下的性能预报提供参考。     

Polynomial expansion for shift- and one- or two-dimensional scale-invariant pattern recognition

A polynomial expansion is suggested for achieving optical invariant pattern recognition. The expansion results in a real function and thus is theoretically able to be implemented under both coherent and spatially incoherent illumination. One obtains the expansion after applying the Gram-Schmidt algorithm on the Laurent's series in order to achieve orthonormality. The initial Laurent term with which we apply the Gram-Schmidt procedure is chosen according to the desired expansion order. The use of the polynomial expansion is demonstrated for shift- and one-dimensional scale-invariant pattern recognition as well as for shift-and two-dimensional scale-invariant recognition.     

Measurement of two-dimensional small rotation angles by using orthogonal parallel interference patterns

Based on measuring one-dimensional small rotation angles by using a parallel interference pattern (PIP), a method for measuring two-dimensional (2D) small rotation angles by using two different PIP's that are orthogonal to each other is proposed. We simultaneously measure the 2D small rotation angles Δθ and Δφ by detecting the phases of the orthogonal PIP's reflected by an object at two detection points. A sensitivity of 4.9 mrad/arcsec and a spatial resolution of 1.5 × 1.5 mm(2) are achieved in the measurement. Theoretical analysis and experimental results show that error ε(1) in the measurement of Δφ is almost equal to -0.01Δθ and error ε(2) in the measurement of Δθ is almost equal to -0.01Δφ. For small rotation angles of less than a few tens of arcseconds, the random errors whose standard deviations are 0.6 arcsec are dominant.     

Modeling of two-dimensional interrelated heat and mass transfer problems and structure transformation

A numerical method to solve interrelated heat and mass transfer problems with structure transformation for easily deformable disperse capillary-porous media is suggested. Structure transformations of bodies of various shape, composition, and capability of cracking during drying are analyzed. Translated from Inzhenerno-Fizicheskii Zhurnal, Vol. 71, No. 6, pp. 1006–1011, November–December, 1998.     

轮毂轴承单元过盈量理论设计及试验研究

针对第3代轿车轮毂轴承单元过盈量的设计,提出了一种考虑铆接装配影响的过盈量理论设计方法.首先,基于弹性力学和平面应力假设推导了轮毂轴承单元内圈与内法兰轴配合的过盈量理论计算式;然后,采用有限元软件建立了轮毂轴承单元过盈装配、铆接装配及铆接卸载回弹过程仿真模型,并通过数值模拟分析获取了其过盈配合面的压力分布及其轴向预紧力...